After the target markets have been established for a medical device, it is critical to review the relevant national deviations to IEC 60601-1. Understanding these deviations enables manufacturers to define the necessary tests and develop a test plan that ensures smooth market entry.
|Robert M. Brown|
A previous article, “A Primer for IEC 60601-1” (MD&DI, September 2003, p. 48) presented an overview of this International Electrotechnical Commission standard and reviewed its importance. This article details some national deviations to IEC 60601-1 and identifies differences between it and the national standards with deviations (see Figure 1).
Because of the national differences, medical device manufacturers need to design and test their products to the worst-case conditions of the tests that apply to the markets in which the products will be sold. Therefore, before completing the design, identifying the target markets for the device is critical. At the design stage, manufacturers should identify all of the compliance tests applicable to the product and necessary for regulatory approval.
IEC 60601 and National Standards
The base standard IEC 60601-1 has been adopted in some form in most major countries (see Table I). The standard, either with national deviations (e.g., JIS T 0601-1 in Japan) or in its orginal form (e.g., in Brazil) is accepted in nearly all markets for supporting regulatory registrations and approvals.
National Deviations. Many national standards are based on IEC 60601-1; however, these standards may contain national deviations. Common deviations include the requirements of the electrical code of the particular country, another national standard that may apply to the product type or its components, and different national component requirements (e.g., modified marking requirements).
Based on national requirements, a national standards-writing body may determine that the international standard is adoptable only by modifying, deleting, or adding requirements. Once the national deviations are made to the standard and the national version of the standard is adopted, the package becomes a national standard with national deviations to IEC 60601-1.
|Figure 1. IEC 60601–1 and national standards with deviations (Click to enlarge).|
Fire has long been identified as a major safety hazard in the United States, where many buildings are constructed of wood. The Great Fire in 1871 that destroyed the central business district of Chicago and the fires at the Columbian Exposition in 1893 caused great concern.
In 1894, William Henry Merrill established Underwriters Laboratories Inc. (UL). An electrical investigator, Merrill was hired by the Chicago Board of Fire Underwriters to investigate the fires that occurred at the Electricity Building during the Columbian Exposition of 1893.
By contrast, in much of Europe, buildings are constructed of brick or stone, so fire is not a prime concern. Electric shock is considered the primary safety hazard and is defined as a higher safety risk than fire in European standards.
U.S. National Differences
|Table I. IEC 60601 national standards (Click to enlarge).|
UL 60601-1 (previously UL 2601-1) is the U.S. national standard for safety testing electrical medical devices. The standard is based on IEC 60601-1 with U.S. national differences. The U.S. national differences are the broadest and most detailed of all the national deviations to IEC 60601-1. The differences are based on a variety of reasons (see Table II), including:
• UL requirements for Recognized Components dealing with fire, shock, and safety hazards. These differences address components that do not have a harmonized IEC component standard. The deviations are identified in UL 60601-1 as DC national differences.
• National Electrical Code (NEC) requirements per NFPA 70, requirements for healthcare facilities and medical installations per NFPA 99, and other regulatory requirements. These deviations are identified in UL 60601-1 as DR national differences.
• Requirements for safety practices. These differences relate to IEC requirements that may be acceptable, but adopting the IEC requirements would require considerable retesting or redesign on the part of the manufacturer. These deviations are identified in UL 60601-1 as D2 national differences.
• Requirements for basic safety principles and requirements, the elimination of which would compromise safety for U.S. consumers and users of products. A deviation based on this criterion is identified in UL 60601-1 as a D1 national difference.
• National differences that are based on editorial comments or corrections. These deviations are identified in UL 60601-1 as DE national differences.
|Table II.UL 60601-1 differences and definitions (Click to enlarge).|
Flammability of Polymeric Enclosures and Covers. UL was formed on the basis of fire safety. The international base standard, IEC 60601-1, does not call out requirements for flammability for polymeric materials. However, the U.S. national deviation in UL 60601-1 refers to the “Standard for Polymeric Materials—Use in Electrical Equipment Evaluations,” UL 746C. UL 746C describes many issues pertaining to polymeric materials.
UL established a flame rating classification for polymeric materials (see Table III). The U.S. national differences in UL 60601-1 require a minimum flame rating of UL 94V-2 for transportable equipment and UL 94V-0 for fixed or stationary equipment. If the fire enclosure is sourced by circuits limited to less than 15 W, flammability requirements are not required. The definitions of transportable, fixed, and stationary are detailed in IEC 60601-1 in Definition Clause 2.
Enclosure Mechanical Abuse Tests. Enclosure mechanical abuse tests are performed to ensure that the enclosure does not expose any live parts or cause a fire, electric shock, or mechanical hazard from these tests. The ball-impact test is an addition to the requirements in IEC 60601-1, and the drop test is a modification of the test requirements called for in IEC 60601-1. The ball-impact test is conducted on the top, sides, and front surfaces of the device under test with an impact of 6.78 N-m or 5 ft-lb.
The drop test is conducted on handheld or hand-guided (i.e., electrode) devices, and each of three samples is to be dropped three times from a height of 1.22 m (4 ft) onto a tile-covered concrete surface. The IEC 60601-1 drop test is from 1 m, and only one sample is dropped three times. Additional mechanical tests deal with end stops.
|Table III. UL 746C flammability ratings (Click to enlarge).|
Leakage Current. The U.S. leakage current deviation is based on the values and requirements of NFPA 99, “Health Care Facilities” and the ANSI/AAMI “Safe Current Limits for Electromedical Apparatus” standards. The differences from IEC 60601-1 modify the acceptable passing limits for the earth and enclosure leakage tests, and maintain the same values for the patient leakage tests.
The base IEC 60601-1 standard does not directly differentiate between inside and outside the patient environment. IEC 60601-1-1, “Medical Electrical Systems,” which addresses a combination of several pieces of equipment, does make a distinction between inside the patient environment and outside it with respect to leakage current testing. UL 60601-1 differentiates between patient-care equipment (6 ft around and 7.5 ft above the patient) and non-patient-care equipment for these leakage current tests. In UL 60601-1, the leakage current values are specified in Tables 19.5DV.1 and 19.5DV.2. These values are given as:
• Class I product (typical value) = 300 µA patient-care area
• Class I product (typical value) = 500 µA non-patient-care area.
UL 60601-1 allows opening of the ground conductor and one of the supply connections simultaneously for non-patient-care equipment. In most cases, the following is true: The earth leakage current test per UL 60601-1 provides the worst-case conditions within the patient area, whereas the enclosure leakage current test per IEC 60601-1 is the worst-case test in the normal condition.
Components. Deviations for UL component standards are defined as DC differences. The modification to the standard shows up in subclauses 3.10DV.1 and 3.10DV.2. These two subclauses call out printed wiring boards, lithium batteries, optical isolators, wiring and tubing, CRTs that are greater than 5 in., and any component in the primary up to the safety isolation transformer.
These components need to meet nationally recognized standards (such as ANSI/UL standards) or internationally harmonized component standards. Annex DVA tabulates UL component standards covering components as specified in subclauses 3.10DV.1 and 3.10DV.2 (see Table IV).
Protective Earthing (Ground Impedance). The U.S. National Electrical Code (NEC) requires that x-ray equipment enclosures and associated equipment have a grounded enclosure around parts that are operating at over 600 V ac, 850 V dc, or 850 V peak. The details are described in added subclauses 18m and 18n.
Conductive Coatings. Conductive coatings are used for electromagnetic compatibility (EMC) shielding to reduce EMC emissions of a product that is made of nonmetallic material (typically plastics). This form of shielding is not as effective as a grounded metal enclosure but can be helpful for a nonmetallic enclosure. Subclause 55DV.2 specifies that conductive coatings applied to nonmetallic surfaces (i.e., plastics) must comply with the applicable requirements in UL 746C, “Standard for Polymeric Materials—Use in Electrical Equipment Evaluations.” These tests are to confirm that the conductive coatings do not flake or peel, reducing spacings or bridging live parts, which could then cause a safety hazard.
Power Supply Cords and Plugs. The U.S. standard requires use of “hospital-grade” or “hospital-only” plugs if a mains hospital-grade plug exists “for the particular electrical rating in question.” In addition, the standard requires mains plugs of nonpermanent equipment with a ground to meet the requirements of UL 498, “Attachment Plugs and Receptacles.”
Any cord-connected equipment that has “hospital-grade” or “hospital-only” attachment plugs “shall be provided with instructions to indicate that grounding reliability can be achieved only when the equipment is connected to an equivalent receptacle marked hospital only or hospital grade. These instructions need to be marked either on the equipment or on a tag on the power cord.
These differences, which are based on the U.S. NEC, are detailed in UL 60601-1 subclauses 57.2DV.1 and 57.2DV.2.
Production-Line Tests. Production-line tests, which are typically a limited number of final tests, are conducted on 100% of the product manufactured. The IEC standard does not prescribe the specific tests and values, times, etc., required, leaving these to the manufacturer's discretion per Appendix A, Rationale, subclause 4.1. To address this, Annex DVB of UL 60601-1 specifies the details for the dielectric voltage withstand, ground continuity, and single suspension system tests.
It is important for manufacturers to read subclause 4.1 closely and talk with their certification agencies to determine appropriate minimums for production-line tests. UL does not require earth and patient leakage current tests, but the Canadian Standards Association (CSA) and most European certification agencies do. Medical device manufacturers should consider conducting this production-line test, even if the device will be sold only in the United States, to ensure that the leakage currents the patient is exposed to are below the requirements of the standard. This issue should be covered in the device manufacturer's risk management of the product.
Canadian National Deviations
|Table IV. UL component standards applicable for UL 60601-1 (Click to enlarge).|
Similar to UL 60601-1 in the United States, CAN/CSA C22.2 No. 601.1 in Canada contains national deviations, which are partially based on the Canadian Electrical Code (CEC). The Canadian standard helps clarify some issues by adding editorial notes helpful to understanding some requirements of IEC 60601-1.
Rub Test Definition. The rub test is conducted on any markings on the unit that are required by the IEC 60601-1 standard. The test is conducted with water, isopropyl alcohol, and methylated spirits. The Canadian standard defines the composition of methylated spirits. It defines methylated spirits as a combination of 90.0% ethanol, 9.5% methanol, and 0.5% pyridine. The definition appears in Appendix A2, subclause 6.1(z).
Ground Impedance Test. The ground impedance test is typically conducted at 30 A for 2 minutes with a maximum no-load voltage of 4 V (based on the Canadian deviation) for medical devices rated up to 15 A. The Canadian standard calls out C22.2 No. 0.4 “Bonding and Grounding of Electrical Equipment (Protective Earthing).” The maximum resistance allowed is 0.1 ? for products that have detachable power supply cords and for permanently wired products.
For a product with a nondetachable power supply cord, the maximum allowed resistance is 0.2 ?. In the IEC standard, the test is conducted at 25 A for units rated up to 16.66 A for 5–10 seconds and a maximum 6 V no-load voltage.
Language Requirements. Clause 6 of the Canadian standard requires that safety instructions on equipment and in accompanying documents be written in both French and English. If the manufacturer is not exporting to a French-speaking province, it is possible that company would not need to provide French translations. However, device manufacturers should verify the spoken language with their certification test house before setting up the labeling and accompanying documentation.
Power Supply Cords and Plugs. Canadian requirements for hospital-grade power cords are similar to those in the United States. The power plug requirements are called out in CSA C22.2 No. 21 and No. 42. These requirements are detailed in subclauses 57.3(b) and 57.2(g) of CAN/CSA C22.2 No. 601.1, respectively.
Gas Connectors and Medical Gas Cylinders. The Canadian deviations are written to avoid any confusion with connection to or use of the proper medical gas. The Canadian standard requires that “the point of connection of gas cylinders to the product is: (i) gas specific, (ii) noninterchangeable, and (iii) identified.” CAN/CSA C22.2 No. 601.1 requires the medical gas inlet connectors on equipment be: (i) gas specific, (ii) noninterchangeable, (iii) of a specific diameter per Compressed Gas Association Pamphlet V-5, and (iv) comply with CAN/CSA Z305.2.
Pressure Vessels. At the publication of the standard, Canadian requirements stated there was no national
regulation dealing with pressure vessels. Each province has different pressure-vessel requirements based partially or wholly on the CSA standard B51, “Boiler, Pressure Vessel, and Pressure Piping Code.”
Japanese National Deviations
|Table V. Leakage current definition per JIS T0601-1 (Click to enlarge).|
The Japanese national deviations to IEC 60601-1 are contained in the JIS T 0601-1 standard. These deviations can be categorized into seven main areas in which the JIS T 0601-1 standard differs from IEC 60601-1.
Reference Standards. For reference standards, JIS T 0601-1 refers to the JIS standards instead of the IEC standards. Some of the JIS standards cited are not compatible with, or do not have, an equivalent IEC standard (e.g., JIS C 0446, “Identification of Conductors by Colors or Numerals”).
Power Cords. JIS T 0601-1 permits alternative colors (white/black) to the international (blue/brown) colors of the conductors for power cords conforming to JIS C 3301. JIS T 0601-1 also restricts the use of vinyl cord (per JIS C 3306) if a metal enclosure is exposed to 60C or higher. JIS T 0601-1 also restricts Class-2 vinyl cord exposed to 75C or higher.
Leakage Currents. The Japanese national standard, JIS T 0601-1, labels leakage currents throughout the document as shown in Table V.
Additionally, one of the main differences between JIS T 0601-1 and IEC 60601-1 is that JIS T 0601-1 does not require an enclosure leakage current measurement to be taken with mains voltage applied on signal input or output parts (SIP/SOP). This is the test in IEC 60601-1 that assumes that the accessory connected to the medical device will fail at mains power.
In IEC 60601-1, this requirement is exempted only if the manufacturer has specified accessories compliant with IEC standards (e.g., IEC 60950 for information technology products) or includes a warning in the manual that users must ensure that devices connected to the device ports (SIP/SOP) comply with IEC standards. The JIS T 0601-1 standard has a more realistic approach.
Also, IEC 60601-1 puts a limit on leakage current, regardless of the waveform and frequency. Leakage current should not exceed 10 mA for frequencies above 1 KHz. JIS T 0601-1 has the same limit, but clarifies that this measurement is to be done directly through a 1-k? noninductive resistor.
Dielectric Tests. JIS T 0601-1 permits the use of 50 or 60 Hz for the dielectric test voltage to check insulation that in normal use is subject to nonsinusoidal voltages.
Collateral Standards. JIS T 0601-1 removes EMC (IEC 60601-1-2) as part of the JIS T 0601 standard. The EMC standard is part of the requirement of the IEC 60601-1 standard (under Clause 36). However, this does not mean that electromedical devices sold in Japan are exempt from EMC requirements. Rather, EMC requirements are addressed separately as part of product approval (Shonin) by the Ministry of Health, Labor, and Welfare. Under JIS T 0601-1, complying with IEC 60601-1-4, the collateral standard for devices that incorporate programmable electronic systems (i.e., software), is optional.
Other Deviations. JIS T 0601-1 effectively reduces the temperature limit of pins on appliance inlets for hot conditions to 120C (from 155C), reserving the higher limit for special conditions.
Australian National Deviations
The Australian national deviations to IEC 60601-1 are contained in Australian Standard AS 3200.1.0. This standard is identical to IEC 60601-1 except that the Australian national deviations are listed in a separate appendix (Appendix ZZ).
Compliance to AS 3200.1.0 is not required under the new Australian Therapeutics Goods (Medical Devices) Legislation (2002). It is possible to register products with the Therapeutics Goods Authority (TGA) using IEC 60601-1 and evaluating medical devices at 240 V, 50 Hz. There are four main areas in which the Australian standard deviates from IEC 60601-1.
Reference Standards. AS 3200.1.0 refers to AS standards rather than IEC standards. For example, AS 3200.1.0 calls out AS 1939 instead of IEC 60529 for degrees of protection provided by an enclosure.
Gas Connection and Gas Cylinders. Similar to Canada, Australia is concerned about confusion associated with the connection of gas cylinders for medical applications. AS 3200.1.0 requires that gas cylinders be marked in accordance with AS 1994, and gas connections (>50 kPa pressure) must comply with AS 2472, AS 2473 or AS 2896, as appropriate.
Suspended Masses. Additional protection for ceiling-supported equipment is required in the AS 3200.1.0 standard. Such equipment includes anticrash devices and brakes or stops that even in single-fault condition do not constitute a hazardous condition. Also required by the AS 3200.1.0 standard is additional protection for floor- and floor-to-ceiling–supported equipment. Such devices include means to inspect cables and anchorages, locknuts, or grub screws for cross arms, pivots, etc.
Power Supply Plugs. Like other nations, Australia requires a provision for inspection of flexible cords fitted with a plug that can be rewired. Plugs are required to be clear-backed to facilitate inspection of the colors and the condition of the termination.
When applying IEC 60601-1, be sure to review all the national deviations. The information included in this article covers just some of the issues that may apply.
Device manufacturers should define their new products' target market before deciding on a test program. Once the target market is established, then the proper national deviations that apply (in addition to IEC 60601-1 tests) can be defined, and test plan that encompasses all the national deviations can be determined.
It is possible that two versions of the same test may be required by different national standards. The worst-case test may be used to represent both, but there are times that both tests are necessary to meet the regulatory requirements of both countries.
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